Filling pore space in a microporous coordination polymer to improve methane storage performance

A strategy that allows the tuning of pore size in microporous coordination polymers (MCPs) through modification of their organic linkers is presented. When large substituents are introduced onto the linker, these pendent groups partially occupy the pores, thus reducing pore size while serving as additional adsorption sites for gases. The approach takes advantage of the fact that, for methane storage materials, small pores (0.4-0.8 nm in diameter) are more desirable than large pores since small pores promote optimal volumetric capacity. This method was demonstrated with IRMOF-8, a MCP constructed from Zn4O metal clusters and 2,6-naphthalenedicarboxylate (NDC) linkers. The NDC was functionalized through the addition of substituents including tert-butylethynyl or phenylethynyl groups. High pressure methane uptake demonstrates that the IRMOF-8 derivatives have significantly better performance than the unfunctionalized material in terms of both excess volumetric uptake and deliverable capacity. Moreover, IRMOF-8 derivatives also give rise to stronger interactions with methane molecules as shown by higher heat of adsorption values.